Stage 17: UI defect fixes (russian variant, Telegram theme/nav/banner, reconnect, hint zoom, plaque, history, transitions, per-game cache)

- #6 align the UI variant id to the backend canonical 'russian_scrabble' (type, variants, Lobby, mock, tests) — fixes the New->Russian 400
- #11/#12 inside Telegram force the colour scheme from WebApp.colorScheme (over OS prefers-color-scheme, fixing the Telegram Desktop breakage) and hide the theme switcher
- #14/#15 nav bar takes Telegram's bg; announcement banner gets a dedicated subtle --ad-bg accent token
- #16 suppress the reconnect banner while backgrounded and silently reconnect the live stream on return to the foreground
- #17 hint zoom scrolls to the placement's bounding box, not the top-left
- #19/#20 players plaque: active seat raised with side shadows, others sunk; tap toggles history
- #21/#23 history: scrollbar-gutter:stable (no word jitter); fixed-height drawer pins the bottom shadow to the board
- #3 (UI) disable nudge on the player's own turn
- #18a directional screen slide transitions (forward in from the right, back reveals the lobby)
- #13 per-game in-memory cache: instant render on re-entry + background refresh
- e2e: openGame waits for the slide transition to settle

ui/src/lib/telegram.ts

@@ -9,6 +9,7 @@ interface TelegramWebApp {
   initData: string;
   initDataUnsafe?: { start_param?: string };
   themeParams?: TelegramThemeParams;
+  colorScheme?: 'light' | 'dark';
   ready?: () => void;
   expand?: () => void;
 }
@@ -48,6 +49,17 @@ export function telegramLaunch(): TelegramLaunch {
   return { initData: w.initData, startParam, theme: w.themeParams };
 }
 
+/**
+ * telegramColorScheme returns Telegram's active colour scheme ('light' | 'dark'),
+ * or undefined outside Telegram. Inside the Mini App this — not the OS
+ * prefers-color-scheme — is the authoritative theme: on some clients (Telegram
+ * Desktop) the OS scheme leaks into the webview and fights Telegram's own setting,
+ * so the app forces this value on launch.
+ */
+export function telegramColorScheme(): 'light' | 'dark' | undefined {
+  return webApp()?.colorScheme;
+}
+
 /**
  * startParamFromURL reads a startapp parameter from the page URL — a bot web_app
  * launch button carries the deep-link there rather than in initDataUnsafe.